This invention relates to solutions of alkali metal stearates which remain soluble and stable at room temperature. In particular, the invention relates to an aqueous solution which includes an alkali metal stearate selected from the group consisting of sodium stearate and potassium stearate, and a water soluble nonionic surfactant. More particularly, the invention relates to a solution which when deposited on a substrate forms a stearate-surfactant lubricant layer upon removal of water. The solutions may be used in neat form or delivered as part of an emulsion.
Alkali metal stearates are blends of an alkali metal and stearic acid, also known as octadecanoic acid, and palmitic acid, also known as hexadecanoic acid. Alkali metal stearates have found a wide use in many product applications. Stearates typically have a "slippery" feel to them which is why they are used in some cases as lubricants and release agents. Stearates are also used as gelling agents, surfactants, thickeners and solidifiers. Generally, 3 to 10 percent of sodium stearate yields sticks having a degree of firmness particularly suitable for deodorant sticks. The mechanism behind stearate solidification and thickening is mentioned in the CRC Handbook of Lubrication pg. 55 as the formation of stearate fibers in solution.
Of all the alkali metal stearates, the sodium and potassium stearates are the only ones that have any water solubility associated with them, all other stearates are essentially water insoluble. However, sodium and potassium stearate are soluble only in water at a temperature about 70.degree. C. At temperatures approaching room temperature, such sodium and potassium stearate solutions become unstable and flocculate out of solution. For example, solutions of sodium and potassium stearate with levels as low as 0.7% sodium and potassium stearate solids become soluble in water heated to 70.degree. C. but upon cooling to room temperature, the solution gels completely.
Accordingly, the need exits for an aqueous solution of alkali metal stearates which is soluble and stable at room room temperature. The term "stable" is defined to mean that no precipitate or gel forms for a period in excess of 90 days.